Date: Sat, 30 Jul 1994 12:24:25 EDT
From: Gary Bourgois
Subject: Re: New Receiver (BUD Only)
Semi s-video faq
S-video is transmitted on two wires. The signal names are luminance or Y,
and chrominance or C. The luminance (Y) carries the video information
without the color. For example, a black and white tv could display a
complete picture with just the luminance (Y) alone. The chrominance
carries the color information of the s-video signals. The phase of the
chrominance signal determines the actual hue, while the amplitude
determines the the saturation of color.
The chrominance signal is 3.58mhz and the luminance is 4.2mhz. Also
these signals are not really Y and C when they come out of the s-video
connector, they must be mixed and amplified in the reciever to drive
the RGB guns, then they become Y and C. These two terms are treated
interchangeably for simplicity by most texts on the subject, although
they are not really the same once they are inside the reciever.
Newer recievers and vcr's incorporate a new circuit called a comb filter.
A comb filter filters out all frequencies that are multiples of 15.734khz
chrominance signal transmission. This filtering results in nearly 25%
increase in horizonal resolution of the pictures, as well as reduction of
unwanted patterns and cross-color effects (noise) in the pictures.
S-video is a standard, so s-video will always deliver a better picture than
composite/baseband signals.
The American video transmission standard NTSC is 525 lines of resolution,
with an aspect ratio of 4:3. Any number of lines may be employed by the
transmitting station usually between 482 and 495.
495.
RokNroB
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From: xerox.com!bf.El_Segundo
Subject: Making the S Connection
In-Reply-To: " "
To: tvro@lopez.marquette.mi.us
Reply-To: xerox.com!bf.el_segundo
Message-Id:
If you will tell me who the keeper of the "(Already too big) FAQ" is, I will
pass this along.
-This was researched from a recent Stereo Review.
"The introduction of Super VHS brought with it a new type of multipin
video connector, called S-video or Y/C. Although the connector itself was a
good idea that has since spread to Hi8 decks and camcorders, its debut in
tandem with S-VHS may not have been, since it has led to some great
misconceptions. Most important among these is the completely erroneous notion
that VCR's equipped with S connectors cannot be used except with similarly
equipped monitors. In fact, all VCR's with S connectors also have the usual
complement of composite-video and RF inputs and outputs and will perform very
nearly as well with those as they will with the S-video inputs and outputs.
The other important misunderstanding is in the idea that the
performance improvements associated with S-VHS are somehow tied to the S-video
connectors. In truth, S-VHS's single benefit-higher resolution-has to do only
with the bandwidth of the signal recorded on the tape, which the S connector
doesn't affect at all. The single benefit of the S connector, on the other
hand, is equally applicable to all consumer VCR formats, "super" or otherwise.
To understand what this is all about, we have to know a little about
how a VCR works. When color was added to television, it was done by putting the
necessary information on a subcarrier plopped into the high-frequency end of
the luminance (black-and-white) signal. Black-and-white receivers ignore this
color (C) subchannel, but color sets extract the information it carries and use
it together with the luminance (Y) information in the baseband signal to
control the intensities of the beams from the three electron guns (for the red,
green , and blue primary colors) in the picture tube. Performing this
separation is not easy, however, and it almost inevitably results in either a
loss of resolution or the creation of small, distracting artifacts, such as as
the "hanging dots" that you may notice from time to time crawling along sharp
horizontal transitions between areas of color.
Professional videotape recorders and laserdiscs record the composite
video signal (Y+C, or luminance plus color) directly, but when home VCR's were
developed, bandwidth and other limitations forced a different approach, known
as "color-under" recording. The color information is separated from the
luminance signal and transposed down to a range of frequencies below those used
for recording the luminance. This degrades the resolution somewhat, but it's
better than going without color.
When a videocassette is played back, the VCR normally recombines the
color and luminance information into a composite-video signal that then goes to
the monitor via a direct-video connection or gets modulated onto an RF carrier
with the audio and sent to the monitor via its antenna terminals. Either way,
the monitor has to reseparate the color and luminance portions of the video
signal. All an S-video connector does is to short-circuit this process,
keeping the luminance and color protions of the signal separate so that they
don't have to be combined and pulled apart again. In most cases, this will
yield a slightly cleaner picture, but the benefit is likely to be marginal, at
best, unless the recorded color and luminance signals have always been
separate, never tangled together in a composite-video signal. Camcorder
recordings fall into this category, but that's about all.
So why do some laserdisc players, which start with a composite-video
signal, have S-video outputs? To prevent consumers from thinking that they lack
a performance feature available on S-VHS and Hi8 VCR's.
The only way a Y/C output can do any good on a laserdisc player is if its
color-separation circuitry happens to be better than that in your monitor,
which is possible but not likely."
Cheers,
Bill
--
/ Gary Bourgois, WB8EOH, The Birdwatcher: Marquette Michigan USA \
([-o Radio Omega G3/17 5.8 - FRIDAY NIGHT LIVE Weekly 9PM Eastern o-])
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